Runout relative to a planar datum

[Belanger]

Since we seem to be having so much fun on the other thread about TIR/runout, let me throw this one out there...

A major company that I work with is floating the idea of allowing GD&T specifications for runout (for now let's just say circular runout) but instead of mentioning a datum axis, as is required per Y14.5, they want to allow a single datum reference of just a flat surface. I of course had to tell them that it's not strictly kosher, but their idea intrigued me.

An everyday example that might help is to think of an old-fashioned pencil sharpener, with the mounting surface attached to a table or on the wall. Imagine that, as you turn the crank, we want to check for runout of the rotating part of the sharpener to determine its relationship to the datum plane formed by the mounting surface.

What are your thoughts? It's not allowed by the current standards, but I suppose it makes sense. Any predictions on whether it will make it into Y14.5 someday?

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[TheTick]

Just........ NO

 

[fsincox]

It is hard for me to say, "no" if you have a real world application that this is used for. I personally do not see it, yet. A pencil sharpener rotates on an axis parallel to a plane?
I generally feel if there is a valid need for something, by design or function, not already covered another way, it is OK. I think Evan said it once, and I felt it was true, we are just trying to describe or uncover how something actually works.
Frank

 

[TheTick]

What about side-to-side movement (parallel to datum plane) of the pencil sharpener?

 

[Belanger]

Tick -- I suppose for that reason total runout would not work, since there is no direction established for the dial indicator to ride along. But circular runout might still work?

Essentially, think of the desired control as equivalent to parallelism, along with circularity. Hey, I don't really like it myself, I just said I was intrigued by their idea...

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[TheTick]

I'm starting to see the light on the potential need for this, however rare it may be. Still, one must be prudent about not creating folklore that masquerades as legitimate GD&T.

 

[MechNorth]

Sounds more like a profile control to locate it wrt the planar datum, maybe with an orientation refinement added in as a composite profile. Plus a basic offset from the planar datum to the feature axis. Checking it, you would essentially use an indicator set at the basic location wrt the datum, then rotate the crank the handle to turn the feature? Remember, though, that a runout control only locates surfaces wrt the axis of generation for the feature ... runout doesn't control the displacement from the datum plane.


Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com